O6-Methylguanine-DNA Methyltransferase Hypermethylation Modulated by 17β-Estradiol in Lung Cancer Cells

Background: Our recent report indicated that MGMT hypermethylation is more common in squamous cell carcinomas (SCC) in males, and smokers than in adenocarcinomas (ADC) in females, and nonsmokers. More interestingly, MGMT hypermethylation in SCC and ADC was pronouncedly influenced by gender factor, not by smoking status. We questioned whether 17 beta-estradiol could modulate the machinery of promoter methylation to cause the gender difference of MGMT hypermethylation in lung cancer. Materials and Methods: Two MGMT hypermethylated Ch27 and H1355 lung cancer cell lines were treated with or without 17 beta-estradiol and the status of hypermethylation was examined by methylated specific methylation (MSP) as compared with both cells treated with demethylating agents, 5-AZA-dC (AZA) or TSA. Results: Our data showed that 17 beta-estradiol, similar to AZA, diminished the MGMT hypermethylation and restored MGMT mRNA expression, which was not observed in the case of TSA. Western blotting showed that 17 beta-estradiol markedly reduced DNMT1 expression in Ch27 and H1355 cells, but slightly reduced HDAC1 expression. Consequently, acetylated H3 and H4 histone levels were slightly increased by 17 beta-estradiol in both cell types. In addition, ChIP analysis revealed that 17 beta-estradiol simultaneously diminished the binding activity of both proteins on the MGMT promoter of both cell lines. Conclusion: 17 beta-Estradiol decreased DNMT1 and HDAC1 protein expressions and their binding activity on MGMT promoter, and this may partially contribute to the gender difference of MGMT hypermethylation in lung cancer.